SACRAMENTO, Calif., April 10 (Reuters) - Californians' approval of their state legislature fell significantly in the days following the arrest of a prominent state senator on corruption and gun-trafficking conspiracy charges, a new poll shows, a toll that may cast a shadow on upcoming elections.

Leland Yee of San Francisco was the third senate Democrat since January to face criminal charges in an ongoing spate of embarrassments for the party, which dominates politics in the most populous U.S. state.

The Field Research Corporation said on Thursday the Yee scandal had caused a three-point decline, to 43 percent, in the number of voters who approved of the job lawmakers were doing. The number of those who disapproved jumped six points to 46 percent.

"The cumulative effect of these scandals has damaged the standing of the legislature in the public's eyes, especially among Republican and non-partisan voters," authors Mark DiCalillo and Mervin Field wrote in their analysis of the poll.

The company was in the midst of asking California voters their opinion on the legislature when Yee was arrested on March 26, sparking an immediate change in respondents' attitudes, they wrote.

The three scandals have cost Democrats a cherished two-thirds legislative majority in an election year and prompted them to cancel a major fundraiser planned for last weekend.

Even before Yee was arrested, fellow state Senator Ron Calderon was indicted on corruption charges and Senator Roderick Wright was convicted of lying about living in the district he sought to represent. All three have been suspended with pay.

The cases hit just as lawmakers in the state are gearing up for major elections next November, when all 80 assembly seats are up for grabs along with many senate seats.

The scandals do not seem to have diminished support for centrist Democratic Governor Jerry Brown, the poll showed. Brown, who is running for re-election, has a 59 percent approval rating, with 57 percent of voters polled saying they would choose him over three Republican candidates.

The survey of 1,000 registered voters was conducted from March 18 to April 5, and has a margin of error of plus or minus 3.2 percentage points. (Reporting by Sharon Bernstein; Editing by Cynthia Johnston)

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